1. Field of the Invention
The present invention relates generally to the fields of disease prophylaxis and therapy. More particularly, it concerns agents that can bind to copper, in certain aspects forming a tripartite complex with protein, and the use of these agents in the prevention and treatment of diseases with a vascular component, such as cancer. Compositions and methods for combination therapy of these diseases, as well as therapeutic kits, are also provided.
2. Description of Related Art
Solid tumors require blood vessel proliferation (angiogenesis) for sustained growth in order to maintain adequate nutrition to other than the most peripheral cell layers (Hayes, 1994; Horak et al., 1993; Parangi et al., 1996). Normal adult human tissues, on the other hand, require little new blood vessel growth, except for wound repair, regeneration following trauma or surgery, and proliferation of the inner lining of the uterus during the menstrual cycle. Thus, dependency on angiogenesis is a fundamental difference between tumor and normal tissue. This difference is quantitatively more striking than the differences in cell replication and cell death rates, on which many cytoreductive chemotherapies depend. As a result of tumor dependency on angiogenesis, the concept of anti-angiogenic therapy for malignancies was developed (Folkman, 1995a; Folkman, 1995b; Hanahan and Folkman, 1996).
Copper is both a requirement and a potent stimulus for angiogenesis, as shown by studies of neovascularization in the rabbit cornea (Parke et al., 1988). During prostaglandin E1 (PGE1)-induced angiogenesis in the rabbit cornea, copper accumulates at the site where angiogenesis occurs (Parke et al., 1988). Conversely, in copper deficient rabbits, angiogenesis in the rabbit cornea in response to PGE1 is greatly reduced. In the rabbit cornea, copper for angiogenesis can be supplied by ceruloplasmin (a copper protein) as well as by dissolved copper sulfate, while apoceruloplasmin (ceruloplasmin without copper) does not support angiogenesis (Gullino, 1986). Additional studies have also shown that copper is an important angiogenic agent (Raju et al., 1982; Ziche et al., 1982). These studies all support the concept that unbound copper is required for angiogenesis.
Several years ago, some animal tumor model studies were carried out using an anti-copper approach (Brem et al., 1990a; 1990b; Yoshida et al., 1995). The chelator penicillamine plus a low-copper diet were used to lower copper levels in rats and rabbits with implanted intracerebral tumors. However, the animals treated with the low-copper regimen, while showing reduction in tumor size, did not show improved survival over untreated controls.
Penicillamine therapy has also been reported to be associated with significant side effects, including nausea and abdominal discomfort, and more serious side effects such as leukopenia and thrombocytopenia, which can lead to aplastic anemia. Nephrotic syndrome has also been reported in certain instances.
There are numerous other examples of diseases characterized by aberrant angiogenesis. One example of such a disease mediated by angiogenesis is ocular neovascular disease. This disease is characterized by invasion of new blood vessels into the structures of the eye such as the retina or cornea. It is the most common cause of blindness and is involved in approximately twenty eye diseases. In age-related macular degeneration, the associated visual problems are caused by an ingrowth of chorioidal capillaries through defects in Bruch's membrane with proliferation of fibrovascular tissue beneath the retinal pigment epithelium.
Another disease in which angiogenesis is believed to be involved is rheumatoid arthritis. The blood vessels in the synovial lining of the joints undergo angiogenesis. In addition to forming new vascular networks, the endothelial cells release factors and reactive oxygen species that lead to pannus growth and cartilage destruction. The factors involved in angiogenesis may actively contribute to, and help maintain, the chronically inflamed state of rheumatoid arthritis.
There remains a need in the art for agents that effectively prevent, slow the onset or progression of, reduce or treat diseases characterized by angiogenesis, such as cancer, macular degeneration, and rheumatoid arthritis. The development of successful prophylactic or therapeutic agents that reduce the level of copper in vivo, without the side effects and risks associated with other copper reducing agents, would represent a particularly significant advance.